Oct. 7, 2004
Donald Savage
Headquarters, Washington
(Phone: 202/358-1727)
Guy Webster
Jet Propulsion Laboratory (JPL), Pasadena, Calif.
(Phone: 818/354-6278)
RELEASE: 03-342
MARS ROVERS PROBING WATER HISTORY AT TWO SITES
NASA's Spirit and Opportunity have been exploring Mars about three
times as long as originally scheduled. The more they look, the more
evidence of past liquid water on Mars these robots discover. Team
members reported the new findings at a news briefing today.
Image left: Opportunity has found new water evidence at this rock,
dubbed "Escher." Click for larger image. Photo credit:
NASA/JPL/Cornell.
About six months ago, Opportunity established that its exploration
area was wet a long time ago. The area was wet before it dried and
eroded into a wide plain. The team's new findings suggest some rocks
may have gotten wet a second time, after an impact excavated a
stadium-sized crater.
Evidence of this exciting possibility has been identified in a flat
rock dubbed "Escher" and some neighboring rocks near the bottom of
the crater. These plate-like rocks bear networks of cracks dividing
the surface into patterns of polygons, somewhat similar in appearance
to cracked mud after the water has dried up here on Earth.
Alternative histories, such as fracturing by the force of the
crater-causing impact, or the final desiccation of the original wet
environment that formed the rocks, might also explain the polygonal
cracks. Rover scientists hope a lumpy boulder nicknamed "Wopmay,"
Opportunity's next target for inspection, may help narrow the list of
possible explanations.
"When we saw these polygonal crack patterns, right away we thought of
a secondary water event significantly later than the episode that
created the rocks," said Dr. John Grotzinger. He is a rover-team
geologist from the Massachusetts Institute of Technology, Cambridge,
Mass. Finding geological evidence about watery periods in Mars' past
is the rover project's main goal, because such persistently wet
environments may have been hospitable to life.
"Did these cracks form after the crater was created? We don't really
know yet," Grotzinger said.
If they did, one possible source of moisture could be accumulations of
frost partially melting during climate changes, as Mars wobbled on
its axis of rotation, in cycles of tens of thousands of years.
According to Grotzinger, another possibility could be the melting of
underground ice or release of underground water in large enough
quantity to pool a little lake within the crater.
Image above: This mosaic of the "Columbia Hills" is the first
360-degree panorama taken since Spirit was there over a month ago.
The dark patch of soil to the right is the spot where Spirit stopped
for engineering work on its right front wheel. This approximate
true-color image, nicknamed the "Cahokia panorama" after the Native
American archaeological site near St. Louis, was acquired between
Aug. 9 and 19. Click for larger image. Photo credit:
NASA/JPL/Cornell.
+ Video: Dr. Jim Bell narrates pan over "Cahokia."
One type of evidence Wopmay could add to the case for wet conditions
after the crater formed would be a crust of water-soluble minerals.
After examining that rock, the rover team's plans for Opportunity are
to get a close look at a tall stack of layers nicknamed "Burns Cliff"
from the base of the cliff. The rover will then climb out of the
crater and head south to the spacecraft's original heat shield and
nearby rugged terrain, where deeper rock layers may be exposed.
Halfway around Mars, Spirit is climbing higher into the "Columbia
Hills." Spirit drove more than three kilometers (approximately two
miles) across a plain to reach them. After finding bedrock that had
been extensively altered by water, scientists used the rover to look
for relatively unchanged rock as a comparison for understanding the
area's full range of environmental changes. Instead, even the
freshest-looking rocks examined by Spirit in the Columbia Hills have
shown signs of pervasive water alteration.
"We haven't seen a single unaltered volcanic rock, since we crossed
the boundary from the plains into the hills, and I'm beginning to
suspect we never will," said Dr. Steve Squyres of Cornell University,
Ithaca, N.Y., principal investigator for the science payload on both
rovers. "All the rocks in the hills have been altered significantly
by water. We're having a wonderful time trying to work out exactly
what happened here," he added.
More clues to deciphering the environmental history of the hills could
lie in layered rock outcrops further upslope, Spirit's next targets.
"Just as we worked our way deeper into the Endurance crater with
Opportunity, we'll work our way higher and higher into the hills with
Spirit, looking at layered rocks and constructing a plausible
geologic history," Squyres said.
Jim Erickson, rover project manager at JPL, said, "Both Spirit and
Opportunity have only minor problems, and there is really no way of
knowing how much longer they will keep operating. However we are
optimistic about their conditions, and we have just been given a new
lease on life for them, a six-month extended mission that began Oct.
1. The solar power situation is better than expected, but these
machines are already well past their design life. While they're
healthy, we'll keep them working as hard as possible."
JPL, a division of the California Institute of Technology in Pasadena,
manages the Mars Exploration Rover project for NASA's Science Mission
Directorate, Washington. Images and additional information about the
project are available from JPL and Cornell at:
http://marsrovers.jpl.nasa.gov
http://athena.cornell.edu
-end-